The present invention concerns concrete slipform paving machines that have a propelling unit or tractor from which a paying kit is suspended with which a layer of concrete is shaped and finished over the underlying ground as the propelling unit travels along a road or airfield alignment. The tractor of a concrete slipform paver has a rectilinear frame which straddles the concrete roadway or airfield pavement section that is being paved. The frame is propelled and supported on either end by crawler tracks mounted on side bolsters. These side bolsters each typically have two hydraulic supporting jacking columns, each of which connects to a crawler track, that allow the tractor frame elevation to be manually or automatically varied relative to the ground. The frame, and in particular a center module thereof, supports a diesel engine-driven hydraulic power unit which supplies power to the tractor and the paving kit.
The paving kit is conventionally suspended below the tractor frame by mechanical means, such as with hooks and a locking mechanism. The paving kit takes its hydraulic power from the power unit on the tractor. The tractor and the paving kit pass over fresh concrete placed in and distributed over its path as a relatively even and level mass that can be conveniently slipform-paved. During this process, the tractor-attached paving kit spreads the semi-solid concrete dumped in the path of the paver, levels and vibrates it into a semi-liquid state, then confines and finishes the concrete back into a semi-solid slab with an upwardly exposed and finished surface. The sideforms mounted on each side of the slipform paving kit shape and confine the sides of the slab during the slipform paving process.
The tractor normally has three or four crawler tracks, each mounted to a jacking column, supporting and propelling the frame during use of the paver in the paving direction. Other kits can be attached to these tractors such as kits for conveying and spreading concrete and trimming and spreading base materials. For the purposes of this description, the focus is on the tractor frame which carries the paving kit.
The length of the tractor frame is adjustable in a transverse direction that is normal to the direction of the paving movement to span different widths of pavements. It is known to use telescopic extensions for changing the length of the frame. Once the telescopic extension limits are reached, a bolt-in, fixed support beam extension can be added to one or both sides of the telescopic frame for further extension.
As is well known, tractor frames for slipform paving machines have a generally rectangularly shaped center module or platform which supports, for example, the power unit including the engine for the paver, an operator platform, and the like. The bolsters that connect the jacking column with the crawlers of the paver are connected to the platform with telescopic extension arms or support beams which can be retracted into the center module, to reduce the length of the paver (in a direction perpendicular to the normal paving direction), or extend it outwardly from the center module, to increase the width for paving. However, the length of the center module limits the distance over which the support beams can be extended away from the center module because a substantial portion of the support beams, typically about three to four feet, must remain secured inside the center module so that the support beams are firmly supported by the center module. It is highly desirable that the paving widths can be adjusted by as much as possible without having to disassemble the tractor frame, and to this end it is known to employ two-stage or double telescopic support beams which, in their collapsed position, nest within each other, as is well known in the art. Thus, there are now slipform pavers on the market which employ a two-stage tractor that can vary the length of the tractor (in a direction normal to the paving direction) over a range between a minimum of about eight feet, three inches (2.5 m) to about twenty feet (6.10 m). If the paver is to lay down a strip of concrete that is wider, it is necessary to partially disassemble the frame to install one or more fixed frame extensions between the ends of the support beams (that are telescoping or not) and the bolsters of the paver to which the jacking columns with the crawlers are mounted. While it is relatively simple and not very time-consuming to change the length of the tractor frame by moving the telescoping support beams in or out, installing bolt-in, fixed support beam extensions to increase the length of the frame past its maximum width attainable with the telescopic support beams significantly increases the time, complexity and difficulty of changing the width of the tractor frame.
Thus, it is highly desirable to construct the tractor frame so that its width can be increased as much as possible with the telescoping support beams to thereby reduce the frequency with which bolt-in, fixed support beam extensions must be installed, which in turn enhances the efficiency and profitability of the paver.
Pavers which employ two-stage, hydraulic, double telescopic extenders with which the maximum length of the tractor frame can be increased without the need for installing fixed frame extensions simplify extending the length of the support beams for a greater paving width. The drawback of such arrangements is that two-stage, hydraulic, double telescopic extenders are complicated, costly to build and maintain, and are difficult to keep from deflecting under vertical loads, thereby reducing the effective paving capability of the paver.